Saturday, March 14, 2009

We industrialize!

Now this is the kind of space advocacy that might actually have a chance of appealing to ordinary folks.

There are none of the supposed "justifications" for the space program that NASA contrived a couple of years ago. There's simply a catchy tune, some simple graphics, and a message. That message is that space offers a tremendous opportunity for us to put our ingenuity and productivity to work towards creating a new and innovative economic niche. This niche is one that has yet to be exploited, has tremendous potential for future growth, and one that we appear to be in a rather unique position to take of advantage of at this very moment.

What will we do with this opportunity? Will we continue to throw good money after bad at sectors of the economy which have failed to generate enough wealth to sustain their own activities? Or do we take bold new steps to generate new industries and new services that will form the basis for the next century of economic growth?

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The ISS as fuel depot testbed

I've been wondering for some time if the ISS could be used to advance the technology required to perfect propellant depot technology. It seems that nearly all of the required hardware is already on board the station. The current ECLSS on the ISS electrolyze waste water and condensate to generate breathable oxygen, with the excess hydrogen being vented to space. If the hydrogen stream could be diverted into a Sabatier reactor, then CO2 could be scrubbed from the atmosphere and turned into methane fuel.

I've also been wondering for if a propellant depot infrastructure should be resupplied with pure water rather than the cryogenic fluids. The favorable density and handling properties of water as opposed to LO2/LH2 would appear to make it the better choice for transporting aboard a very simple tanker over potentially long time periods. When shipped as water, the "fuel" can be transported in a non-cryogenic, inert state, and then once delivered to the depot, it can be cracked into O2/H2, liquefied, and stored until it is needed.

Of course, this assumes that your depot has sufficient power and/or time to split water and keep the fuel properly chilled. I found this page which describes the Russian Elektron unit. This article cites a passage from a NASA training manual:


From the “NASA Familiarization Manual on Russian Segment Crew Systems”, Published in 1997.

3.1. Oxygen Supply System
The decomposition of 1 kg (2.2 lbs) of water yields 25 L (0.88 ft3) of oxygen per hour at a pressure of 760 mmHg, which is enough to support one crew member for one day. To provide the daily amount of oxygen for 3 - 4 crew members, 3 - 4 kg (6.6 - 8.8 lbs) of water must be decomposed. Power consumption of the process is ~ 1 kW.

A kilogram per hour at one kW, seems like a very reasonable rate, at that's just for one Elektron unit (if I'm reading this correctly). If necessary, this can scaled up with additional units if sufficient power is available. It may be possible to build even more power efficient electrolysis system if the work of Dr. Nocera at MIT can be turned into a practical device that will operate in zero-G conditions.

If the depot is also crewed, then a steady supply of water would be required any way. The crewed depot could also generate methane as an additional propellant option if the ECLSS included a Sabatier reactor as well as an electrolysis unit. With the exception of the Sabatier reactor and some cryogenic storage tanks, the ISS already possesses all of the hardware. The existing U.S. electrolysis units even have hardware available for connecting to a Sabatier reactor.

So, what would be the point of having the ISS generate and store propellant? Well, first of all, it is currently our only manned research outpost in zero-G. It would therefore be expedient to take advantage of these facilities to work out the basics of cryogenic fluid transfer in micro-gravity. The data obtained from ISS experiments could go along way towards reducing the techological risks associated with propellant depot development.

The ISS also needs fuel for station-keeping. Having the ability to generate it's own propellant would be a nice capability to have. This would also simplify the ISS resupply requirements. Rather than having to deliver water and propellant, each in the individual compartments, only water would be required. The water tanks could be made larger, and therefore more mass efficient. Since propellants would no longer need to be transported (I think hypergolics are currently used), the handling of the payload for resupply missions would be much less hazardous.

Finally, with the ability to produce fuel, the ISS could support a small array of space tugs and transfer vehicles which would service the station and other objects in nearby orbits. For example, imagine that SpaceX puts up a couple of Dragon lab modules in orbits which are coplanar with the ISS. Now imagine that the ISS has a slightly modified ATV docked to it. It might then be possible for an ISS astronaut to use the ATV to rendezvous with the Dragon module and perform any necessary maintenance or repairs.

I have some additional thoughts on how to convert the ATV into a crewed orbital transfer vehicle, but I think I'll save those for another post.

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Sunday, March 08, 2009

A Biological Imperative

Every few months, the debate over humans in space seems to flare up again. The motivations for human spaceflight are usually touched on briefly while reflecting on the loss of the astronauts of the Apollo I, Challenger, and Columbia spacecraft. Sometimes the discussion is sparked by the humans vs. robots debate. Other times it shows up while attempting to justify the human spaceflight budget. Depending on the context and the participants, the discussion can be anywhere from cordial to an outright flame war.

Jeff Foust recently posted a fairly innocuous summary of reactions to the new administration's budget request (Reacting to the budget proposal - Space Politics) which has somehow managed to stir up a fair amount of discussion in its comments. Unfortunately, by the time I got around to reading through it, some of the comments had already began devolving into pointless bickering.

Of course, I felt compelled to post some of my own thoughts. I am reposting them here for my own benefit, and in case anyone would like to discuss them away from the flames of the other post.

Human space exploration is not about science, or even exploration for that matter. These things are a consequence - a side effect - of having humans in space. In fact, science and exploration are a consequence of humans being just about anywhere, including the bottom of the ocean or in caves dozens of kilometers below the surface. Humans will make observations (either directly or through remote probes), form hypotheses, test them, and then find a way to exploit the results somehow. That's what humans do.

The question on everyone's mind is "Why?" Why do we go to all of these extreme places (in person and with probes)? The answer is quite simple: niche exploitation and expansion. It's a biological imperative. We do what biological organisms have always done: expand to fill an available niche, exploit resources where possible, and then search for new niches to fill. In every biological population, there are individuals or groups which make it their purpose to accomplish each of these tasks. Humans are particularly adept at this and are doing so at an unprecedented rate.

What makes humans so special is that they are the first species capable of expanding the biosphere beyond the surface of the Earth. Humans alone are capable of taking this simple biological imperative out into the universe; exploiting the resources found there, remaking the environment to sustain themselves, and always pressing forward. It is for this purpose that the robotic probes are made and sent out in advance; and that robotic machines are being created to assist humans in hostile environments. It is also for this reason that we cannot send robotic probes alone.

In a way these thoughts are complementary to those I have posted previously (Why Space? and Not Just Science). I find that my thoughts have evolved somewhat since then. I have been trying to come to a better understanding of what it is that space advocates are trying to articulate when they give the 'basic human need to explore' argument. Although most space advocates feel this in their bones, they usually fail to give an adequate explanation of this feeling to those who do not necessarily share their passion for space. I'm not saying that my comments above will go much further at bringing this point home to the average Joe. However, I do feel that if we can get past our own personal motivations and cast human spaceflight in a broader context, we may eventually be able to convince others that it is well worth the expense.

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